母牛的发情周期平均为多少天？

母牛的发情周期平均为21天，处女牛一般少1～2天，母牦牛发情周期平均为20.5天，变动范围为17～25天。发情周期受光照、温度、饲养管理、劳役、个体情况等因素影响，分为发情前期、发情期、发情后期和休情期。发情持续时间指从母牛愿意接近公牛开始至回避爬跨的期间，母牛平均为18小时，范围6～36小时，个别可达48小时。母牦牛发情持续期为12～36小时。季节、饲养管理条件、年龄等因素影响发情持续时间，夏季、饲养条件好和经产家在户户戶户戶门户门户关关系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系和企业企业企业企业企业企业企业企业企业企业企业企业企业企业企业企业企业企业企业企业黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土黄土勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞勞访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访访家园和田责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制责任制为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先为先